docs: add RustFS and Restic integration guide

[majinghe]

Add a new RustFS + Restic backup integration section under Developer > Integration in all supported locales.

Changes:

• Add a new Backup landing page and Restic guide in en/de/fr/ja/zh.
• Update integration navigation for each locale.
• Add localized Console screenshots under each locale's backup images directory.

Validation:

• npm run docs:check
• npm run build

Note:

• The provided Console credentials could not authenticate on the shared RustFS instance, so the captured screenshot is the Console login screen rather than the post-login Console view.

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